Decaffeination by commercial techniques often involves solvent extraction from whole green beans such as described by Patel et al. in U.S. Pat. No. 3,671,263 who use a chlorinated hydrocarbon solvent, and by Berry et al. in U.S. Pat. No. 2,309,092 who use a caffeine-deficient solution of coffee solubles. Also of commercial importance is the extraction of caffeine from aqueous solutions with a water-immiscible solvent as described by Adler et al. in U.S. Pat. No. 2,933,395. However, each of these procedures affect the quality of the beverage and there is an effort being made to enable the use of alternative solvents or eliminate the need for solvent/product contact. For example, in Belgian Pat. No. 835,556, there is disclosed a process wherein aqueous caffeine solutions are contacted with liquid, water-immiscible fatty extractants at ratios of liquid extractant to caffeine solution of about 20:1. The high volumes of extractant seriously detract from the commercial utility of such a process because of the high added costs.
In an alternative to the use of highly caffeine-specific solvents, Katz suggests in U.S. Pat. No. 4,113,886 that a selective membrane can be employed to effect separation. The solvent functions only to transfer the caffeine from the feed solution to an aqueous phase for collecting the extracted caffeine.
As a total alternative to liquid extractants, a number of patents teach solid adsorbents. For example, U.K. Pat. No. 1,488,340 describes removing caffeine from an aqueous solution by means of polymeric non-ionogenic adsorption resins. While certain of these resins are effective and produce high quality products, they remain more costly than desired. Other patents, such as U.S. Pat. No. 2,391,981 and U.S. Pat. No. 2,416,484 to Kremers, discuss clay as an adsorbent, however, clay is not satisfactorily selective for commercial use as such. Similarly, the hydrated silicates as disclosed by Grossman in U.S. Pat. No. 2,375,550 remove valuable coffee solids other than caffeine. Other patents, such as U.S. Pat. No. 2,472,881 to Bender, U.S. Pat. No. 2,508,545 to Shuman, and U.S. Pat. No. 4,168,324 to Roselius et al., disclose the attraction of caffeine by activated carbon. However, none of these patents suggest decaffeination of an aqueous extract by direct contact with activated carbon because the activated carbon is not specific to caffeine and picks up many other solids.
Thus, the prior art attempts with liquid extractants need improvement, but the available systems employing solid adsorbents are either too costly or not suitably selective. Accordingly, there is a present need for improvement by means of an alternative process for decaffeination.